Devices such as a warp knitting machine, a loom and a warping machine operate on many rows of line up yarns for knitting, weaving, winding, sizing, etc., while the yarns are being supplied. When even one of the yarns in a row of line up yarns breaks, the devices must immediately detect it and stop the operation; otherwise defective articles are produced.
The warp knitting machine and the loom usually have a dropper type detection feeler; each of the warps is provided with a dropper and when a warp breaks, the dropper falls due to its own weight. The falling of the dropper causes the machine to stop either mechanically or electrically.
Warp knitting machines and looming machines run at remarkably high speeds. The above dropper type detection feeler is too time-wasting and inefficient because it needs a preparatory process of inserting warps through each dropper, and furthermore this feeler easily malfunctions owing to improper dropper fall or bad electrical contact, thereby failing to fully work as a monitoring/controlling means for these recent, high-speed machines.
Under these circumstances, a photoelectric feeler has come into use because it is more responsive and capable of monitoring the status of a warp and controlling a machine without contacting a warp. One photoelectric feeler in a broken yarn detection system includes a light emitter and a light receiver disposed at opposite ends of a row of warps so that the axis of emitted light coincides with that of the light receiver, and an alarm is sent out when a broken warp crosses the emitted light to interrupt the received light. This type of photoelectric feeler is likely to malfunction under the influence of ravellings and other floating things, and consequently fails to be a reliable monitoring means for line up yarns consisting of many warps.